FRI are a very poor way of retaining personnel. If pilots want to go let them. The market is self regulating. Once MoD paid the first FRI they made a rod for their own back. I know many who took the money, stayed for the minimum time and left anyway. Others had no intention of leaving. Thus on balance a waste of money.
When I was a lad we joined out of sense of duty and did not constantly look over the fence to see if the grass was greener.